1. Field of the Invention
The present invention relates to a balanced oscillator and an electronic apparatus including the same, and more specifically to a balanced voltage-controlled oscillator for use as a local oscillator in a cellular telephone, for example, and an electronic apparatus including the balanced voltage-controlled oscillator.
2. Description of the Related Art
In communication devices such as cellular telephones, oscillators such as voltage-controlled oscillators are used as local oscillators. Recently, with the popularity of integrated circuits within communication devices, the adoption of balanced signal processors has increased due to its resistance to common mode noise in its signal paths, and the demands for balanced oscillators capable of obtaining a balanced output have also increased.
FIG. 4 is a circuit diagram of a balanced oscillator 1 of the related art. In FIG. 4, the balanced oscillator 1 includes a differential oscillator circuit 2 and a differential amplifier circuit 3.
The differential oscillator circuit 2 includes transistors Q1 and Q2, resistors R1 and R2, capacitors C1, C2, and C3, inductors L1 and L2, varactor diodes VD1 and VD2, and a constant current source I1. The transistor Q1 has a collector connected with a d.c. power supply Vdc via the inductor L1, and a base connected with a bias power supply Vb via the resistor R1. The transistor Q2 has a collector connected with the d.c. power supply Vdc via the inductor L2, and a base connected with the bias power supply Vb via the resistor R2. The emitters of the transistors Q1 and Q2 are connected with each other and are also connected with a ground via the constant current source I1. The base of the transistor Q1 is connected to the collector of the transistor Q2 via the capacitor C1, and the base of the transistor Q2 is connected to the collector of the transistor Q1 via the capacitor C2. The collectors of the transistors Q1 and Q2 are connected with each other via the capacitor C3. The collector of the transistor Q1 is further connected to a control voltage input terminal Vc via the varactor diode VD1, and the collector of the transistor Q2 is also connected to the control voltage input terminal Vc via the varactor diode VD2.
In the differential oscillator circuit 2 of such a structure, the transistors Q1 and Q2 are cross-connected with each other via the capacitors C1 and C2 to perform differential oscillation at a frequency defined by the capacitance of the capacitors C1 through C3, the inductance of the inductors L1 and L2, and the capacitance of the varactor diodes VD1 and VD2. The differential oscillator circuit 2 has two outputs led from the collectors of the transistors Q1 and Q2. As is anticipated from the fact that the differential oscillator circuit 2 includes the varactor diodes VD1 and VD2, the differential oscillator circuit 2 is a voltage-controlled oscillating circuit; however, this is not an essential point to the present invention and a description thereof is thus omitted.
The differential amplifier circuit 3 includes transistors Q3 and Q4, and a constant current source I2. The transistor Q3 has a collector connected with the d.c. power supply Vdc, an emitter connected with an output terminal P1, and a base connected with the collector of the transistor Q1. The transistor Q4 has a collector connected with the d.c. power supply Vdc, an emitter connected with an output terminal P2, and a base connected with the collector of the transistor Q2. The emitters of the transistors Q3 and Q4 are connected with each other and are also connected with the ground via the constant current source I2.
The differential amplifier circuit 3 of such a structure receives and differentially amplifies the two differential output signals of the differential oscillator circuit 2. The differential amplifier circuit 3 has two outputs led to the output terminals P1 and P2 from the emitters of the two transistors Q3 and Q4, respectively.
In the balanced oscillator 1 of the related art, the differential oscillator circuit 2 and the differential amplifier circuit 3 are connected in parallel to the d.c. power supply Vdc in an independent manner. This requires separate constant current sources for driving the differential oscillator circuit 2 and the differential amplifier circuit 3, thus making it difficult to achieve low current consumption.
In order to overcome the foregoing problem, the present invention provides a compact balanced oscillator with low current consumption, and an electronic apparatus including the balanced oscillator.
In an aspect of the present invention, a balanced oscillator includes a differential oscillator circuit having two output terminals, and a differential amplifier circuit having two input terminals each being connected with each of the two output terminals of the differential oscillator circuit. The direct-current path of the differential oscillator circuit is connected in series with the direct-current path of the differential amplifier circuit.
Either one of the differential oscillator circuit and the differential amplifier circuit may be connected so as to operate as a constant current source of the other.
In another aspect of the present invention, an electronic apparatus includes the above-noted balanced oscillator.
Therefore, a balanced oscillator according to the present invention and an electronic apparatus including the balanced oscillator can achieve low current consumption and size reduction.
Other features and advantages of the present invention will become apparent from the following description of embodiments of the invention which refers to the accompanying drawings.